31 killed in airstrikes by rebel groups in Syria

At least 31 people were said to be killed by airstrikes carried out by warplanes on rebel-held districts in Aleppo, a monitor group reported.

Warplanes carried out four airstrikes on Sunday on the rebel-held neighbourhoods of Qaterji, Sukkari and Bab al-Naser as well as other areas in eastern Aleppo, Xinhua news agency quoted Syrian Observatory for Human Rights as saying.

At least 10 families are stuck under the rubble, which could likely raise the death toll, the UK-based watchdog group added.

The Observatory, which says it relies on a network of activists on ground, accused the government forces of being behind the airstrikes and the shelling.

Meanwhile, battles continued between the Syrian army and an array of ultra-radical rebel groups in Aleppo, amid reports of a progress made by the government forces in the Khan Tuman area, according to the Observatory.

On the international arena, the United States and its partners were mulling to impose sanctions on Syria and Russia over the situation in Aleppo.

"We are pursuing diplomacy because those are the tools we have," said US Secretary of State John Kerry following a meeting on Sunday with the foreign ministers of Britain, France and Germany in London.

"I do not see a big appetite in Europe for people to go to war," he said.

This comes amid heightened tension between Washington and Moscow over Aleppo, particularly after the Syrian government forces have tightened the siege on eastern Aleppo with the help of Russia, and urged the rebels there to surrender.

Aleppo, has been a focal point of clashes between the Syrian army and the rebels.